The resonant nonlinear optical (NLO) response and excited-state dynamics of pure and photochemically modified ${\mathrm{C}}_{60}$ are studied at 590.5 nm by time-resolved degenerate four-wave mixing and nonlinear transmission. The magnitude of the NLO response for ${\mathrm{C}}_{60}$ is largely unaffected by photopolymerization or oxygen doping. The presence of molecular oxygen shortens the unimolecular lifetime of the participating excited states while photopolymerization appears to alter the character of the fluence-dependent kinetics. Bimolecular decay via exciton-exciton annihilation dominates the temporal response at high-fluence for ${\mathrm{C}}_{60}$, poly-${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{60}$-${\mathrm{O}}_2$ films. The bimolecular rate coefficient $k_2$ determined for ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{60}$-${\mathrm{O}}_2$ films is 7×${10}^{-9\mathrm{}}$ ${\mathrm{cm}}^3$/s with an uncertainty on the order of a factor of 2.

• Received 25 October 1994

DOI:https://doi.org/10.1103/PhysRevB.51.11376